1. Field of the Invention
The present invention relates to a photocurable pigment type inkjet ink composition, and more particularly to a photocurable pigment type inkjet ink composition including a reactive surfactant.
2. Description of the Related Art
Early inkjet printers used water-based ink that included the water-soluble solvent. The inkjet printing method involves printing a water-based ink onto an ink-absorbent substrate, such as paper or a substrate coated with an ink-receiver layer. The printed image is fixed by penetration, absorption and drying of the ink. Water-based ink suffers from long drying time and it cannot be printed on a non-ink-absorbent substrate such as a glass, plastic, metal, or ceramic substrate. In addition, the printed image has poor water fastness and may partially dissolve upon contact with moisture.
A photo-curable type (ultraviolet-curable type) inkjet ink has been developed to improve the above-mentioned disadvantages. A photo-curable type inkjet ink includes at least a pigment, a dispersant for the pigment, a photocurable (photopolymerizable) component (such as a monomer, resin, or oligomer), an emulsifier for emulsifying the photocurable component, and a photoinitiator that is introduced into the ink by emulsion or dissolution. The photo-curable type inkjet ink is printed onto a substrate and fixed after irradiation (UV ray, IR ray, or electron beam). Thus, a printed image can be fixed on ink-absorbent substrates, and also non-ink-absorbent substrates such as glass, plastic, metal, or ceramic substrates. Thus, the adhesion of the pigment to the substrate, and the water fastness and smear resistance of the image are improved.
Generally, in a pigment type inkjet ink, the average particle size of the pigment is less than 200 nm. Therefore, a suitable dispersant together with milling equipment must be used to turn the pigment particles into microparticles suitable for inkjet printing. The microparticle pigment dispersant solution requires good dispersion stability to prevent nozzle clogging due to pigment agglomeration during printing. In addition, a photocurable component must be blended into the ink by emulsion or dissolution.
Both the dispersant for dispersing the pigment and the emulsifier for emulsifying the photocurable component affect the surface tension and the viscosity of the ink, which in turn affects the inkjet printing properties of the ink.
R.O.C. Patent No. 271464 discloses a dispersant that can dissolve the photocurable resin. Japanese Patent No. 09165540, U.S. Pat. No. 5,952,401, and Japanese Patent No. 2001288386 also disclose non-photocurable dispersants. U.S. Pat. No. 6,326,419 uses a non-photocurable emulsifier for emulsifying a UV-curable monomer or oligomer.
In the above conventional techniques, the dispersants and emulsifiers used in the photocurable inkjet ink are non-photocurable (non-reactive), that is, they cannot react by irradiation. Therefore, the non-reactive dispersant or emulsifier remains in the printed image and acts as a plasticizer. This adversely affects the adhesion of the printed image to the substrate, and the smear resistance of the printed image.